Molds are used for many purposes, such as the shaping of synthetic resins, where in order to create objects of expanded synthetic resins, a relatively small amount of the material is injected into the interior of the mold. The material subsequently expands and assumes the shape of the inner surface of the mold. It is therefore desirable that the mold should be hermetically sealed and, where synthetic resins are used, it is not possible to employ elastomer joints between the mold parts since such seals would be very quickly destroyed by the materials being handled. It is therefore the practice to close the mold by pressing together rims on the mold parts.
At present the locking of molds in their closed position is effected by means of mechanical devices uniformly spaced about the mold periphery and acting on the rims of the two parts of the mold, in order to ensure air-tight closure thereof. Usually the mechanical devices used are eccentrics of toggles.
The disadvantage of such devices is that they produce a force-characteristic curve with an asymptotic shape. Consequently the travel of a locking hook engaging the rims is very limited. Moreover they have a degree of play in the region of the joint plane which should be taken up. This makes it necessary to provide special play-take-up devices and requires frequent adjustment by the operator. Furthermore if the dimensions of the locking devices vary, a poor distribution of the forces between the mold parts is produced, thereby rendering production of an air-tight closure unreliable.